1. Field of the Invention
The present invention relates to a glass article having a surface-protection coating and method for producing the glass article with the surface-protection coating, and in particular, to material of the surface-protection coating which can be easily washed off.
2. Description of the Related Art
During storage and handling operation of glass articles such as plate glass, bottle glass, tube glass and glass for electronic parts, those glass articles come often into contact with other glasses or another member and thereby suffer from surface scratches, and/or often contaminated by dust, dirt, moisture, or others which will be collectively called xe2x80x9cdirtxe2x80x9d. The scratches or dirt are likely to cause product defects.
Even an invisible miniscule amount of contamination is not permitted, particularly for glass requiring high surface quality such as glass for cathode-ray tubes and glass substrates for flat panel displays, and glass for displays to which various types of surface treatments are performed in a following process. Due to the deposit of organic contaminants or the like in a small quantity, a finishing agent coated on a glass article in a later process cannot be wetted well but is repelled on the glass surface, thereby deteriorating film characteristics of the finishing agent.
As an example of those glass articles, there is known a cathode-ray tube (CRT). Referring to FIG. 1, the CRT comprises a panel glass 10, which has a generally rectangular face part 10a forming an effective screen and a skirt part 10b, a funnel-form funnel glass 11 attached to this panel glass 10 by sealing with frit glass (not shown in the figure), and a tube-form neck glass 13 joined to the funnel glass 11 and having an electron gun 12 attached therein. Electron beams from the electron gun 12 make a fluorescent film 14 on an inner surface of the panel glass 10 emit light to project images on the face 10a of the panel glass 10. Additionally, a metallic anode button 15 is attached as an anode terminal at a predetermined location on the funnel glass 11, and a reinforcing band 16 is mounted around the skirt part 10b of the panel glass 10 so as to maintain strength and to prevent scattering at the time of breakage. There are provided an aluminum film 17 so as to prevent the return of fluorescence from the fluorescent film 14, a shadow mask 18 so as to regulate the irradiation location of electron beams, stud pins 19 so as to fix the shadow mask 18, and a carbon film 20 so as to prevent high charge by electron beams of the shadow mask 18 and to be electrically continued and grounded outside.
The carbon film 20 is on inner and outer surfaces of the funnel glass 11 formed by applying carbon slurry, called dag thereon. However, when an invisible miniscule amount of organic contaminant is deposited on glass surfaces in storing or handling the funnel glass 11 before the application of carbon slurry, hydrophilic groups on the glass surfaces decrease. As a result, carbon slurry is likely to be repelled, and thus a uniform carbon film 20 cannot be easily formed.
Moreover, although a metallic oxide film is formed on the surface of the anode button 15, this film is likely to be contaminated with organic substances or the like because the film has higher surface free energy than the surrounding glass part. When organic contaminants deposit on the surface of the anode button 15, an adhesive property between the carbon film 20 and the anode button 15 becomes weak in applying carbon slurry and the carbon film 20 is likely to be easily peeled off. If the carbon film 20 on the surface of the anode button 15 peels off, functions would deteriorate for funnel glass for cathode-ray tubes, which thus causes serious problems.
Therefore, funnel glass for cathode-ray tubes is pre-washed with corrosive acid such as sulfuric acid, nitric acid and hydrofluoric acid, and strongly alkaline sodium hydroxide or the like to completely remove contaminants such as organic substances deposited on the surface of glass and an anode button, before coating carbon slurry to form a carbon film on inner and outer surfaces of the funnel glass.
However, since the liquid is highly harmful and dangerous, such a cleaning method requires meticulous care in handling cleaning liquid and is highly troublesome in treating the waste liquid, and also costly.
Particularly when contaminants adsorb on the surface of an anode button, the adsorption force of the contaminants is very strong. Therefore, complete removal of the contaminants must be made by polishing with an abrasive material, heating at high temperature of 400 to 500xc2x0 C. for thermal decomposition, or washing over a long period with acid or alkali as mentioned above.
On the other hand, in the production of bottle glass or the like, there has been used a method where sulfurous acid gas or the like is blown onto a surface of hot glass products to thereby deposit onto the surface bloom as a reaction product with sodium in glass, by which glass surface scratches and cullet adhesion can be prevented.
This bloom is water-soluble and easily removable with water. However, this method has problems in that sulfurous acid gas corrodes peripheral devices. The reaction product is unlikely to deposit when there is a small amount of alkali in glass. It is also difficult to precisely control the amount and deposit conditions of the product.
Accordingly, in order to solve the above-noted problems, Japanese Unexamined Patent Publication (JP-A) No. H06-340865 proposes the coating of a surface-protection film made of water-soluble salts on the surface of a glass article. When the surface-protection film is washed out from the glass article, the contaminants deposited thereon can also be removed together with the surface-protection film. The surface-protection film is made of sodium tripolyphosphate, sodium sesquicarbonate and sodium tetraborate as examples disclosed therein. However, they are alkali materials, so that when a glass article is stored for a long period after coating the material on the glass article surface to form a surface-protection film, an alkali component in the surface-protection film gradually corrodes a glass surface, thus damaging the appearance of the article.
Moreover, such a surface-protection film of water-soluble salts is physically formed through precipitation of crystals on the glass surface and is therefore formed like small islands on the sea. Thus, when the film is reduced in its thickness, it is difficult to uniformly coat the film over the glass surface. Accordingly, the glass surface may often be contaminated because the glass surface would come into direct contact with a packaging material, sebum or the like during storage in a packaging box over a long period, thus contaminants adhering onto the glass surface.
Particularly, sodium tripolyphosphate and sodium tetraborate contain phosphorus and boron and therefore may damage living things and the environment. Therefore, a treatment facility is also required for treating waste liquid of them.
It is an object of the present invention to provide a glass article having a uniform and dense water-soluble surface-protection film applied on its glass surface for effectively protecting the glass surface from scratches, contamination, and corrosion even over a long period of storage. The surface-protection film may be easily washed off with water, and the waste liquid is quite safe for living things and the environment.
Further, it is another object of the present invention to provide a method for producing the glass article, as well as a method for cleaning the glass article.
A glass article of the present invention comprises a glass body having a glass surface and a water-soluble surface-protection coating applied onto a predetermined area of the glass surface, the water-soluble surface protection coating is made of a material comprising hydroxy acid or salt thereof.
A method of manufacturing a glass article of the present invention comprises: preparing a glass body having a glass surface for the glass article; preparing an aqueous solution of hydroxy acid or salt thereof; applying the aqueous solution onto a predetermined area of the glass surface to form a thin film of the aqueous solution on the predetermined area of the glass surface; and drying said thin film of the aqueous solution to form a dried film of the hydroxy acid or salt thereof.
A method of cleaning an article surface according to the present invention comprises: applying and drying an aqueous solution containing hydroxy acid or salt thereof to the article surface to form a water-soluble surface-protection film made of a material comprising hydroxy acid or salt thereof, and washing off the water-soluble surface-protection film together with contaminants deposited on the surface-protection film.